4.6. Enabling Versioned Views

As noted in 4.2. Release Type Options, SNOMED CT data can be imported into database tables from snapshot release files, from full release files or from both these sets of release files. The objective of importing the data into the database is to provide effective access to useful views of that data. In practical terms this means facilitating access to some or all of the views summarized in .

View	Content Description	Use Cases	Value
Current Snapshot	The most recent version of each SNOMED CT component and reference set member.	All practical uses of the current version of SNOMED CT	Essential for any use of SNOMED CT
Retrospective Snapshot	The most recent version of each SNOMED CT component and reference set member released prior to a specified earlier snapshot time.	A baseline against which to review of changes to SNOMED CT during or after installing a new release. Review of health records taking account of the version of SNOMED CT at the time the data was recorded. Comparative analysis of health record data collected at different times taking account of changes to SNOMED CT.	Valuable
Most Recent Delta View	The latest version of each SNOMED CT component and reference set member added, changed or inactivated in the most recent release. Typically, all these items with have an effectiveTime equal to the most recent release date. However, in cases where interim releases are made available between releases, the most recent delta view may be specified as including all items with an effectiveTime after the previous major release date.	Identification of changes to SNOMED CT arising from the most recent release.	Valuable as an indicator of recent changes
Other Delta Views	The versions of each SNOMED CT component and reference set member added, changed or inactivated after a specified delta start time and at or before a specified delta end time.	Identification of changes to SNOMED CT over a period of time.	Useful for longer term monitoring of changes.
Delta Views with Details of Changes	The content of a specified delta view combined with the retrospective snapshot view of SNOMED CT components and reference set members in the delta view at the specified delta start time.	Reviewing full details of changes to SNOMED CT between two releases or over a period of time. Assessing and managing the impact of updates to SNOMED CT.	Required for effective change management

summarizes the way in which different release type options affect the ability to access particular snapshot and delta views of SNOMED CT data. Importing the snapshot release supports direct access to the current snapshot view and query access to the most recent delta view. The full release provides access to all snapshot and delta views but is likely to perform slightly less well with the current snapshot view. Importing both full and current snapshot releases offers all the advantages of importing the full release and also provides direct access to the current snapshot view. This combined option requires more storage capacity but may be worthwhile because the current snapshot is likely to be the most commonly used view.

	Release Types Imported
Views Supported	Current Snapshot	Full	Full & Current Snapshot
Current Snapshot View	Direct	Query	Direct
Retrospective Snapshot Views	Not supported	Query	Query
Most Recent Delta View	Query	Query	Query
Other Delta Views	Not supported	Query	Query
Delta Views with Details of Changes	Not supported	Query	Query

The following subsections explore specific mechanisms that can be used to deliver these views in a relational database.

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